It's hard to say for sure. Some might be based on real events, but often there's an element of exaggeration or fictionalization for entertainment purposes.
It varies. Some Hollywood series are directly inspired by true events and try to stick closely to the facts. Others take elements from real life and build a fictional story around them. And then there are those that are purely made up for entertainment.
Mostly no. The show takes creative liberties and combines fictional characters and plotlines with some general themes and settings associated with Hollywood, rather than being strictly based on true stories.